1. Technical Field
This invention relates to a patch antenna that is primarily used for mobile communications or wireless local area networks (LAN), and to electronic equipment that utilizes the same.
2. Description of Related Art
As a small planar antenna for mobile communication or wireless LAN, a microstrip antenna or a patch antenna with a thickened strip has been widely used. FIG. 6 shows an exemplary structure of such a patch antenna. In the example shown in FIG. 6, a patch antenna 51 comprises a dielectric plate 52, a ground plate 53 provided on entire one surface of the dielectric plate 52, a patch 54 provided on the other surface of the dielectric plate 52, and a feeding line 55 provided on the other surface of the dielectric plate 52 for connection to the patch 54. Further, a numeral 56 shows a feed point for feeding power to the feeding line 55 and ground plate 53.
The patch antenna 51 of the aforesaid structure has an advantage that it is small and thin, hence, it does not take a large space. However, in case of using it as an antenna for mobile communication such as mobile computing or as an antenna for wireless communication for connecting a computer to a network, there have been problems in that it has not only narrow directivity due to the ground plate 53 provided on one surface of the dielectric plate 52, but also a narrow frequency bandwidth due to a high Q value. Namely, if such a patch antenna has narrow directivity and yet narrow frequency bandwidth, it is required to direct the antenna toward its communication counterpart at the time of wireless communication, or to specify a direction of the antenna at the time of installing electronic equipment such as a computer. Apparently, these problems have rendered such a patch antenna impractical. To this end, what has been desired in the field of mobile communication or wireless LAN is to improve the conventional patch antenna such that it is substantially non-directional and yet it has a broader frequency bandwidth.
On the other hand, a technique has been proposed to provide an aperture on a patch antenna for lengthening its current path, thereby to downsize the antenna. It is also known to provide an aperture on the ground plate, thereby to feed power from a strip line to the antenna by means of electromagnetic coupling. Further, Japanese Patent Publication 10-22723 discloses a technique for forming notches on a ground electrode (ground plate) to suppress a distinctly polarized wave; Japanese Patent Publication 10-233617 discloses a technique for improving an inverted-F shaped planar antenna by making use of a ground plane with an aperture (ground plate); and Japanese Patent Publication 7-46033 discloses a technique for forming a pair of slots on a ground plane element (ground plate) to provide a two-frequency or multifrequency capability. However, even with these techniques, it has been unable to implement the non-directional and broad-bandwidth characteristics of a patch antenna.
Therefore a need exists for a patch antenna having non-directional and broad-bandwidth characteristics.